U.S. patent application number 13/201012 was filed with the patent office on 2012-02-09 for telecommunication network.
This patent application is currently assigned to Eutelsat S A. Invention is credited to Antonio Arcidiacono, Daniele Vito Finocchiaro.
Application Number | 20120034915 13/201012 |
Document ID | / |
Family ID | 40957691 |
Filed Date | 2012-02-09 |
United States Patent
Application |
20120034915 |
Kind Code |
A1 |
Arcidiacono; Antonio ; et
al. |
February 9, 2012 |
TELECOMMUNICATION NETWORK
Abstract
A network for establishing RF links between a main ground
station connected to a NOC center and ground terminals via a
multispot satellite, the network being composed of a coverage area
composed of a plurality of cells in which terminals are located,
each cell being associated with at least one link spot beam with
the satellite to which a frequency band is allocated, the center
including a determination module to determine the transmission
parameters characteristic of the position of terminals in the
coverage area, the parameters covering the entire coverage area and
a transmitter to transmit all parameters to each of the terminals.
Each of the terminals includes a storage device to store at least
part of all the parameters, a positioning device to determine its
geographic position in the coverage area and a processor to
determine, from the parameters and its geographic position, the
transmission parameters to be utilized.
Inventors: |
Arcidiacono; Antonio;
(Paris, FR) ; Finocchiaro; Daniele Vito; (Paris,
FR) |
Assignee: |
Eutelsat S A
Paris
FR
|
Family ID: |
40957691 |
Appl. No.: |
13/201012 |
Filed: |
February 5, 2010 |
PCT Filed: |
February 5, 2010 |
PCT NO: |
PCT/EP10/51451 |
371 Date: |
October 26, 2011 |
Current U.S.
Class: |
455/430 |
Current CPC
Class: |
H04W 52/243 20130101;
H04W 16/28 20130101; H04W 52/241 20130101; H04B 7/18513
20130101 |
Class at
Publication: |
455/430 |
International
Class: |
H04W 4/02 20090101
H04W004/02; H04B 7/185 20060101 H04B007/185 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 11, 2009 |
FR |
0950854 |
Claims
1. A telecommunication network for establishing radiofrequency
links between at least one main ground station connected to an
operating center of said network and ground terminals via a
multiple spot beam telecommunication satellite, said network
comprising: a multispot satellite; at least one main ground
station; a plurality of ground terminals, said ground terminals
being located in a plurality of cells that form a coverage area,
each cell being associated with at least one spot beam with said
satellite to which a frequency band is allocated; an operating
center of said network connected to said main ground station, said
operating center comprising: a determination module configured to
determine, at all times, transmission parameters characteristic of
a position of said ground terminals in said coverage area, said
transmission parameters covering the entire coverage area, a
transmitter configured to transmit to each of said ground terminals
all transmission parameters determined by said determination
module, each of said ground terminals comprising: a positioning
device configured to determine a geographic position of said ground
terminal in said coverage area, a storage device configured to
store at least part of said set of transmission parameters, a
processor configured to determine the transmission parameters to be
used by said ground terminal from said stored part of said set of
transmission parameters and from said geographic position.
2. The network according to claim 1, wherein said transmission
parameters are determined by said determination module to reduce
cross interference between said cells.
3. The network according to claim 1, wherein said positioning
device configured to determine the geographic position in said
coverage area of the ground terminals from among said plurality of
ground terminals comprises: a device including a satellite
positioning system; a positioning device using wireless access
points; a positioning device based on one or more cellular type
base stations; an absolute positioning device such as measuring the
ground magnetic field or the wattage of known radio stations; or a
relative positioning device such as an inertial positioning
system.
4. The network according to claim 1, wherein said positioning
device is configured to determine the position of said ground
terminal with an accuracy of less than one order of magnitude to
the size of the cell in which the ground terminal is located.
5. The network according to claim 1, wherein said determination
module is configured to periodically determine said transmission
parameters.
6. The network according to claim 5, wherein the updating period is
between 1 and 1440 minutes.
7. The network according to claim 5, wherein periodic updating is
carried out by taking a state of said network into consideration
from data obtained in real time on the position of the ground
terminals in said coverage area.
8. The network according to claim 1, wherein at least one cell is
associated with at least two link spot beams with said satellite, a
frequency band being allocated to each of said two spot beams, such
that said determination module determines the frequency band to use
within said cell so as to reduce cross interference between the
cells forming the coverage area.
9. The network according to claim 1, wherein said determination
module is configured to determine, at every update, for every
coverage area, the frequency channel to be used by the terminals
according to their position in said coverage area, each frequency
band being broken down into frequency channels.
10. The network according to claim 9, wherein said determination
module is configured to determine, at every update, the type of
modulation to be used by the terminals according to their position
in said coverage area.
11. The network according to claim 1, comprising a plurality of
main ground stations, each main ground station being connected to
said operating center of said network.
12. The network according to claim 1, wherein said determination
module is configured to determine a group of acceptable
transmission parameters for each of the geographic positions.
13. The network according to claim 12, wherein said processor
configured to determine the transmission parameters to be utilized
by said ground terminal is configured to select the transmission
parameters to be utilized according to a probability distribution,
in the group of acceptable parameters for said terminal.
14. The network according to claim 12, wherein said processor
configured to determine the transmission parameters to be utilized
by said ground terminal is configured to select the transmission
parameters to be utilized according to the particular limitations
of said ground terminal, in the group of acceptable parameters for
said terminal.
15. The network according to claim 12, wherein said group is
determined from said geographic position of said ground terminal by
said processor.
16. The network according to claim 1, wherein said transmission
parameters are determined by said determination module by
considering factors including an intermodulation between different
frequency bands on board the satellite; or a measured sensitivity
of a satellite antenna for each coverage, or both.
17. The network according to claim 1, wherein said storage device
of said ground terminal is configured to store all of the
transmission parameters.
18. An operating center of a network according to claim 1, said
operating center comprising: a determination module configured to
determine, at all times, transmission parameters characteristic of
the position of said ground terminals in said coverage area, said
transmission parameters covering the entire coverage area, a
transmitter configured to transmit to each of said ground terminals
all transmission parameters determined by said determination
module.
19. A ground terminal for implementing a network according to claim
1, said terminal comprising: a positioning device configured to
determine a geographic position of said ground terminal in said
coverage area, a storage device configured to store at least part
of said set of transmission parameters, a processor configured to
determine the transmission parameters to be used by said ground
terminal from said stored part of said set of transmission
parameters and from said geographic position.
Description
[0001] The present invention relates to a telecommunication network
for establishing radiofrequency links between at least one main
ground station connected to a network operating center and ground
terminals via a multispot telecommunication satellite. This type of
satellite enables the use of several spot beams on board the
satellite to cover many geographic areas or cells, instead of a
single large spot beam.
[0002] Such multispot satellites enable several radiofrequency
links occupying the same frequency band on different spot beams to
be established.
[0003] In the case of a high bandwidth broadband satellite
telecommunication system, the satellite is used bidirectionally,
which is to: [0004] relay data sent by a main ground station
(connected to a Network Operating Center or NOC) to a plurality of
ground terminals: this first point to multipoint type link
constitutes the forward link; [0005] relay data sent by the ground
terminals to the main ground station: this second multipoint to
point type link constitutes the return link.
[0006] An example of such a multispot telecommunication network 1
is illustrated in FIG. 1.
[0007] This network 1 comprises: [0008] a plurality of main ground
stations 2 such as communication gateways; [0009] a NOC center 5;
[0010] a plurality of ground terminals 6; [0011] a multispot
satellite 3.
[0012] The main ground stations 2 (also called central stations
below) are connected to the NOC center 5 (typically via the
Internet). The NOC center 5 is a network management system that
allows the operator to monitor and control all the components in
the network.
[0013] In return link, the signals are sent to the multispot
satellite 3 over an uplink LM by the ground terminals 6. The
signals sent by the ground terminals 6 are then processed at the
level of the satellite 3 payload that amplifies them, derives the
signals at a generally lower frequency and then retransmits the
signals from the satellite antenna or antennas on a downlink LD in
the form of a plurality of spot beams to ground stations 2.
[0014] The forward link from the ground stations 2 to the ground
terminals 6 operates identically with an opposite communication
direction. The coverage area in which the ground terminals are
located is broken down into basic coverage areas or cells. Each
cell is associated with at least one spot beam from the multispot
satellite.
[0015] Network 1 such as represented in FIG. 1 uses a technique
known as the frequency reuse technique: This technique allows the
same frequency range to be used several times in the same satellite
system in order to increase the total capacity of the system
without increasing the allocated bandwidth.
[0016] Frequency reuse schemes, known as color schemes (where each
color corresponds to a frequency band), assigning one color to each
of the satellite spot beams, are known. These color schemes are
used to describe the allocation of a plurality of frequency bands
to the satellite spot beams in view of radiofrequency transmissions
to carry out in each of these spot beams. In these schemes, each
color corresponds to one of these frequency bands.
[0017] In addition, these multispot satellites enable polarized
transmissions to be sent and received: The polarization may be
linear (in this case the two directions of polarization are
respectively horizontal and vertical) or circular (in this case the
two directions of polarization are respectively left circular or
right circular).
[0018] However, such a configuration is likely to pose several
difficulties.
[0019] Typically, in the case of a communication uplink between a
ground terminal and the multispot satellite, the satellite serves
the entire coverage area that includes a plurality of basic cells.
Each of the cells is individually illuminated by an antenna spot
beam from the multispot antenna on the satellite. A frequency band
is associated with each cell and, within each frequency band; many
different frequency channels are available for the ground terminals
operating in these cells. A ground terminal of a first cell thus
operates on a slot or channel from the frequency band associated
with said first cell. It will be noted that in the case of the
utilization of a transmission coding system based on the spread
spectrum of the CDMA (Code Division Multiple Access) type, many
terminals from the same cell may use one and the same channel at
the same time.
[0020] The user terminal also operates in a specific time interval
for the channel utilized. The uplink departing the user terminal is
directed in the main spot beam of the multispot antenna that serves
the cell. This main spot beam also comprises multiple lateral
lobes. Consequently, interference of the common channel may also be
transmitted by the ground terminal to the lateral lobes of another
spot beam serving another cell using the same frequency band. This
cross interference phenomenon between cells is explained by the
fact that the multispot antenna may not completely control its
reception characteristics. The interference signal that arrives at
the lateral lobes, even at a power level lower than the power level
of the main signal, constitutes interference leading to signal
degradation.
[0021] A known solution that reduces this cross interference
phenomenon between cells is described in patent document EP0999662.
According to this document, before transmitting, the user terminal
sends a service request to the NOC center. The latter has a user
database comprising various parameters. Each time the NOC receives
a request from a user terminal, it determines for this user
terminal a transmission parameter (typically the frequency slot and
the temporal slot over which the terminal will transmit) then it
transmits this transmission parameter to the user terminal.
[0022] However, such a solution according to the prior art presents
two major disadvantages.
[0023] First, the process as described in document EP0999662
necessarily implies that the terminal opens a connection with the
NOC (via sending a request) to inform it that it wishes to
establish communication and to obtain the transmission parameter.
Sending this request thus brings about an additional delay, which
may prove to be detrimental.
[0024] In addition, this process effectively leads to the use of
part of the frequency band available for sending requests. This
utilization of the band is independent from the type of
communication that the terminal seeks to establish. Therefore,
particularly for terminals transmitting small-size messages at a
high frequency, the process will bring about a high and
unacceptable bandwidth capacity occupation. For example, this is
the case with POS "Point of Sale" type fixed terminals that
transmit short messages with a high transmission frequency or
mobile terminals sending text messages (emails or SMS).
[0025] In this context, the present invention aims to provide a
telecommunication network for establishing radiofrequency links
between at least one main ground station connected to an operating
center of said network and ground terminals via a multispot
telecommunication satellite, said network reducing cross
interference while preventing high consumption of the available
frequency band and reducing processing delays.
[0026] For this purpose, the invention proposes a telecommunication
network for establishing radiofrequency links between at least one
main ground station connected to an operating center of said
network and ground terminals via a multiple spot beam
telecommunication satellite, known as a multispot satellite, said
network comprising: [0027] a multispot satellite, [0028] at least
one main ground station, [0029] a set of ground terminals, [0030] a
coverage area composed of a plurality of cells in which said ground
terminals are located, each cell being associated with at least one
spot beam with said satellite to which a frequency band is
allocated, [0031] an operating center of said network connected to
said main ground station, said network being characterized in that
said operating center comprises: [0032] means for determining, at
all times, transmission parameters characteristic of the position
of said ground terminals in said coverage area, known as
optimization means, said transmission parameters covering the
entire said coverage area, [0033] means for transmitting to each of
said ground terminals all transmission parameters determined by
said optimization means, each of said ground terminals comprising:
[0034] means for determining its geographic position in said
coverage area, [0035] means for storing at least one part of said
set of transmission parameters, [0036] Means for determining the
transmission parameters to be used by said ground terminal from
said stored part of said set of transmission parameters and from
said geographic position.
[0037] Ground terminal is understood to refer to a terminal that
may be fixed, transportable or mobile.
[0038] Main ground station (gateway) is understood to refer to any
central station such as a ground communication gateway connected to
the operating center, typically via an Internet backbone.
[0039] Operating center is understood to refer to a NOC "Network
Operating Center" that constitutes a network management system that
allows the operator to monitor and control all network
components.
[0040] Thanks to the invention, the NOC operating center optimizes
the overall performance of the network for the entire coverage area
(typically by reducing to the maximum cross interference between
the cells of the coverage area). The NOC thus has optimized
transmission parameter (i.e., all of the transmission parameters)
mapping for the entire coverage area. This mapping particularly
comprises a frequency (as well as other parameters) allocation plan
to be used by the terminals. The NOC then transmits this mapping to
all ground terminals in the network according to the invention, by
preferentially using a single "broadcast" transmission
(simultaneous transmission to all terminals). The mapping is
regularly updated according to variations in the network operating
conditions.
[0041] Each ground terminal receives this mapping, which is stored
in the terminal storage means and updated with every new
transmission by the NOC. To minimize the quantity of storage
necessary, the terminal may store only the part of the mapping that
is necessary to the terminal (typically the part corresponding to
its current position and the vicinity of this position).
[0042] When the terminal wants to send a message, it starts by
locating its position via means utilizing, for example, a GPS
system; it executes some software means enabling it to determine,
from its position and stored mapping, the transmission parameters
(frequency band, frequency channel within this band, polarization,
time slot, modulation, code, etc.) to be used to send this message.
Contrary to the known networks in prior art, the terminal therefore
does not have to send a request to the NOC to obtain its
transmission parameters.
[0043] The network according to the invention may also present one
or more of the characteristics below, considered individually or
according to all technically possible combinations: [0044] said
transmission parameters are determined by said optimization means
to reduce cross interference between said cells; [0045] said means
for determining the geographic position in said coverage area of
the mobile terminals from among said set of ground terminals are
chosen from among the following means: [0046] means using a
satellite positioning system (GPS, EGNOS, Galileo, etc.); [0047]
positioning means using wireless access points (WIFI, WiMax, etc.);
[0048] positioning means based on one or more cellular type base
stations (GSM, UMTS, etc.); [0049] absolute positioning means such
as measuring the ground magnetic field or the power received from
known radio stations; [0050] relative positioning means such as an
inertial positioning system; [0051] said means for determining the
geographic position in said coverage area are such that they enable
said ground terminal to determine its position with an accuracy of
less than one order of magnitude to the size of the cell in which
the ground terminal is situated; [0052] said optimization means
periodically determine said transmission parameters; [0053] the
updating period is between 1 and 1440 minutes depending on the
speed of network state change; [0054] periodic updating is
performed by taking the state of said network into consideration
from data obtained in real time on the position of the terminals in
said coverage area; [0055] at least one cell is associated with at
least two link spot beams with said satellite, a frequency band
being allocated to each of said two spot beams, such that said
optimization means determine the frequency band to use within said
cell so as to reduce cross interference between the cells forming
the coverage area; [0056] said optimization means comprise means
for determining, at every update, for every coverage area, the
frequency channel to be used by the terminals according to their
position in said coverage area, each frequency band being broken
down into frequency channels; [0057] said optimization means
comprise means for determining, at every update, the type of
modulation to be used by the terminals depending on their position
in said coverage area; [0058] the network according to the
invention comprises a plurality of main ground stations, each main
ground station being connected to said operating center of said
network; [0059] said optimization means determine a group of
acceptable transmission parameters for each of the geographic
positions; [0060] said means for determining the transmission
parameters to be used by said ground terminal select the
transmission parameters to be used according to a probability
distribution, in the group of acceptable parameters, for said
terminal; [0061] said means for determining the transmission
parameters to be used by said ground terminal select the
transmission parameters to be used according to the particular
limitations of said ground terminal, in the group of acceptable
parameters for said terminal; [0062] said group is determined from
said geographic position of said ground terminal by said means for
determining the transmission parameters; [0063] said transmission
parameters are determined by said optimization means by taking into
consideration such factors as: [0064] the intermodulation between
different frequency bands on board the satellite; [0065] the
measured sensitivity (G/T figure) of the satellite antenna for each
coverage; [0066] Said storage means of said ground terminal store
all transmission parameters.
[0067] Another object of the present invention is a network
operating center according to the invention, said operating center
comprising: [0068] means for determining, at all times,
transmission parameters characteristic of the position of said
ground terminals in said coverage area, known as optimization
means, said transmission parameters covering the entire said
coverage area, [0069] means for transmitting to each of said ground
terminals all transmission parameters determined by said
optimization means.
[0070] In addition, the object of the present invention is a ground
terminal for implementing a network according to the invention,
said terminal comprising: [0071] means for determining its
geographic position in said coverage area, [0072] means for storing
at least one part of said set of transmission parameters, [0073]
means for determining the transmission parameters to be used by
said ground terminal from said stored part of said set of
transmission parameters and from said geographic position.
[0074] Other characteristics and advantages of the invention will
clearly emerge from the description given below, for indicative and
in no way limiting purposes, with reference to the attached
figures, among which:
[0075] FIG. 1 is a simplified schematic representation of a
multispot configuration network;
[0076] FIG. 2 is a simplified schematic representation of a network
according to the invention;
[0077] FIG. 3 represents a coverage area composed of a plurality of
cells;
[0078] FIG. 4 represents the coverage area of FIG. 3 with a first
frequency plan;
[0079] FIG. 5 represents the coverage area of FIG. 3 with a second
frequency plan.
[0080] In all figures, common elements bear the same reference
numbers.
[0081] FIG. 1 has already been described above with reference to
the reminder of the prior art.
[0082] FIG. 2 is a simplified schematic representation of a network
100 according to the invention.
[0083] This network 100 comprises: [0084] a plurality of main
ground stations 102 such as ground communication gateways; [0085] a
NOC center 105; [0086] a plurality of ground terminals 106 that may
be mobile terminals but also fixed terminals (as an illustration, a
single ground terminal 106 is represented here); [0087] A multispot
satellite 103.
[0088] The ground terminal 106 is equipped with: [0089] an antenna
110, [0090] a GPS "Global Positioning System" terminal 113,
enabling it to know its position via LGPS links with satellites 109
at all times, [0091] a modem 111 allowing it to transmit and
receive data during exchanges with the multispot satellite 103;
[0092] storage means 112 (database); [0093] management means 114;
[0094] Input/output interface means 115 (keypad, speaker,
etc.).
[0095] Management means 114 typically comprise a microprocessor
controlled by programs situated in a program memory. The program
memory is notably intended for the management of different
operations to be executed to implement different functionalities of
terminal 106. The memory comprises several software means (i.e.,
applications), some of which are dedicated to implementing the
invention. In other examples of embodiment, these software means
may be replaced by specific electronic circuits.
[0096] The main ground stations 102 (also called central stations)
are connected to NOC center 105, typically via an Internet
backbone.
[0097] In return link, the signals are sent to the multispot
satellite 103 over an uplink LMR by the ground terminals 106. The
signals sent by the ground terminals 106 are then processed at the
level of the satellite 103 that, via its payload, amplifies them,
derives the signals at an appropriate frequency, then retransmits
the signals from the satellite antenna or antennas on a downlink
LDR in the form of a spot beam or a plurality of spot beams to the
ground stations 102.
[0098] The forward link, including uplinks LMF and downlinks LDF of
ground stations 102 to ground terminals 106, operates identically
with an opposite communication direction.
[0099] The coverage area in which the ground terminals are located
is broken down into basic coverage areas or cells.
[0100] The configuration of the network 100 according to the
invention as represented in FIG. 2 utilizes a technique known as
the frequency reuse technique. This technique allows the same
frequency range to be used several times in the same satellite
system in order to increase the total capacity of the system
without increasing the allocated bandwidth.
[0101] For each cell, it is possible to use at least one frequency
band corresponding to part of the available bandwidth. Each
frequency band is associated with a spot beam from the multispot
satellite. Each frequency band may be broken down into a plurality
of frequency channels. A ground terminal 106 will use a frequency
channel to transmit; this same terminal 106 will also operate in a
particular time interval (temporal slot).
[0102] According to the invention, the NOC center 105 comprises
means 108 for determining a mapping of the coverage area with a
determination of the transmission parameters characteristic of the
position of the ground terminals in the coverage area. These
determination means 108 will be subsequently designated by the term
"optimization means." The transmission parameters typically include
the frequency band, the frequency channel, the temporal slot and
the type of modulation or code to be used by the terminals
depending on their position in the coverage area. The mapping is
comprehensive; in other words, the mapping includes the
transmission parameters for the entire coverage area: These
transmission parameters are determined by the optimization means
108 so as to reduce the cross interference between cells and to
maximize system performance. It will be noted that several sets of
parameters may be acceptable for the same location.
[0103] Typically an initial mapping (we will return to this point
later with reference to FIGS. 4 and 5) is provided to the
optimization means 108. The mapping is transmitted to all ground
terminals 106 in network 100 and then is stored by each of the
ground terminals 106 in its storage means 112.
[0104] Henceforth, when a terminal 106 wants to establish a
connection, it starts by locating its position via its GPS
positioning system 113. Management means 114 of terminal 106
comprise a software application allowing the determination, from
its position and stored mapping, of the transmission parameters
(frequency band, frequency channel within this band, time slot,
modulation, polarization, level, code, FEC, etc.) to be used to
establish this connection, by choosing from among the possible
parameters defined by the mapping. In case of a plurality of
acceptable sets of parameters, the choice, from among the
acceptable parameters, may be made depending on the limitations of
the terminal, such as the type of terminal or type of message that
will be sent, and/or randomly according to an appropriate
probability distribution (possibly sent by NOC 105 with the
mapping).
[0105] According to a particularly advantageous embodiment of the
invention, optimization means 108 determine a new mapping based on
real-time data collected from main ground stations 102, said data
concerning the current position of ground terminals within the
network. When the mapping is updated by optimization means 108, the
mapping update is transmitted to all ground terminals 106. The
updating period is typically between one minute and several hours,
depending on how fast the network state is changed. However, in the
absence of a mapping update, the old mapping is sent bit by bit to
benefit the terminals that were not listening before (terminals
that were powered off, or lacking satellite reception).
[0106] Optimization means 108 typically utilize combinatorial
algorithms so as to determine the best possible mapping for
reducing cross interference between cells. In other words,
optimization means 108 will determine the mapping that allows the
maximum amount of data to be transferred from ground terminals 106
to ground stations 102 via satellite 103 while minimizing the
impact of cross interference generated by different cells.
[0107] An example of a coverage area 200 is illustrated in FIG. 3.
This area 200 covers part of Europe and groups together 6 cells C1
to C6 in the case of a multispot configuration of the return link
in band S at 2 GHz for satellite Eutelsat W2A. This example is
given for purely illustrative and in no way limiting purposes.
Satellite W2A has 15 MHz of global frequency band for each
direction. Table 1 below mentions the countries associated with the
centers of cells (in other words, each of these countries allows a
cell to be identified).
TABLE-US-00001 TABLE 1 C1 C2 C3 C4 C5 C6 Spain Great Britain France
Italy Poland Germany (SP) (UK) (FR) (IT) (PL) (G)
[0108] It will be noted that the cells present overlapping areas.
The terminals of the network according to the invention know their
transmission parameters independently of the cell or cells in which
they are located; according to a preferential embodiment of the
invention, it is important that each terminal may determine its
position with an accuracy of less than one order of magnitude to
the size of the cell in which the ground terminal is situated
(typically an accuracy of around 50 km for a cell of 500 km of
diameter).
[0109] For each cell, in the case of W2A, it is possible to utilize
up to two frequency bands, each having a width of 5 MHz from among
the 15 MHz of available band. Each frequency band is associated
with a spot beam from the multispot satellite. In the case of an
FDMA type protocol, each 5 MHz-frequency band is broken down into a
plurality of frequency channels. In the case of a CDMA type
protocol, each band represents a single channel that may be
utilized at the same time by a limited number of terminals.
[0110] In each 5 MHz frequency band, a ground terminal will utilize
a channel for transmission.
[0111] FIG. 4 represents the coverage area of FIG. 3 with a first
frequency plan 300 that constitutes a frequency plan adapted for
being implemented without using a network according to the
invention. This first frequency plan 300 obviously takes a certain
number of restrictions into consideration. It will be noted that
each 5 MHz frequency band is associated with a blue, yellow or red
color in a frequency reuse scheme, also called a color scheme:
[0112] the color blue is represented by close-together hatched
lines and corresponds to frequency band B; [0113] the color red is
represented by spaced-apart hatched lines and corresponds to
frequency band A; [0114] the color yellow is represented by dots
and corresponds to frequency band C.
[0115] Without using the invention, one is obligated to allocate
frequencies (from among the 12 total bands possible, that is to
say, 2 bands for each of the 6 cells) according to a suboptimized
plan to avoid interference. Typically in the case of plan 300, only
8 bands are utilized from among the 12 possible bands with a total
bit rate of 50 Mbps. This frequency plan 300 is determined a priori
from combinatorial algorithms so as to determine the best possible
mapping for reducing cross interference between cells. Table 2
indicates the frequencies associated with different countries in
the coverage area.
TABLE-US-00002 TABLE 2 Great Britain France Poland Germany Spain
(SP) (UK) (FR) Italy (IT) (PL) (G) B (referenced A and C A and B C
(referenced B (referenced C (referenced by (referenced (referenced
by by by SP-B) by UK-A by FR-A IT-C) PL-B) G-C) and UK-C) and
FR-B)
[0116] This limitation to 8 possible bands is connected to the
desire to limit interference: As an example, it is impossible to
use frequency A in Italy because there would be too much
interference from English terminals "further south" on cell C4
covering Italy, and from Italian terminals "further north" on cell
C2 covering Great Britain (the interference is not necessarily
symmetrical).
[0117] The network according to the invention allows some of these
restrictions to be dispelled. FIG. 5 represents the coverage area
of FIG. 3 with a second frequency plan 400 that constitutes a
frequency plan that may be implemented at a certain time by
utilizing the network according to the invention. Again, each 5 MHz
frequency band is associated with a blue, yellow or red color in a
frequency reuse scheme. [0118] the color blue is represented by
close-together hatched lines and corresponds to frequency band B;
[0119] the color red is represented by spaced-apart hatched lines
and corresponds to frequency band A; [0120] the color yellow is
represented by dots and corresponds to frequency band C.
[0121] According to the invention, by considering the case of a
uniform distribution of terminals on the territory and by utilizing
data from the satellite, typically antenna data, optimization means
108 may establish a more optimal frequency use plan: According to
FIG. 5, the same frequency band A is utilized on cells C4 and C2
respectively covering Italy and Great Britain inasmuch as this band
A will only be utilized by the ground terminals at the locations
where less interference is generated. Typically in the case of plan
400, 11 bands are utilized from among the 12 possible bands with a
total bit rate of 92 Mbps (or an increase of 80% with relation to
the possible rate in the case of frequency plan 300 of FIG. 4).
Table 3 indicates the frequencies associated with different
countries in the coverage area.
TABLE-US-00003 TABLE 3 Great Britain France Poland Germany Spain
(SP) (UK) (FR) Italy (IT) (PL) (G) B and C A and C A and B A and C
B and C C (referenced (referenced (referenced (referenced
(referenced (referenced by by SP-B by UK-A by FR-A by IT-A by PL-B
D-C) and SP-C) and UK-C) and FR-B) and IT-C) and PL-C
[0122] An example of embodiment of optimization means 108 is based
on the incremental optimization of a starting configuration.
[0123] A starting configuration for the system is initially set
according to the following steps: [0124] 1. the overall coverage
area is partitioned into several coverage areas (that do not
overlap), normally smaller than the size of the spot beams utilized
by the satellite; [0125] 2. for each area identified, a spot beam
is chosen that must receive signals transmitted by the terminals
found therein; [0126] 3. For each area, a set of parameters is
fixed by being based on the known characteristics of the satellite
(antenna radiation diagrams, power, transponder frequency, etc.)
and by utilizing heuristics to maximize the expected performance of
the system (for example, reusing the same frequency range in areas
that are sufficiently far apart).
[0127] As an example, European coverage W2A was partitioned into 11
areas; for each area, the spot beam covering it with the maximum
G/T antenna gain to noise temperature value was chosen to serve
this area; then, a frequency range and polarization were assigned
to each area, so as to respect satellite constraints and space
apart areas with the same pair (frequency, polarization) as much as
possible.
[0128] As mentioned above, by dynamically exploiting the network
according to the invention, the frequency plan (i.e., the mapping,
including the trans-mission parameters to be utilized by the ground
terminals) will be regenerated by optimization means 108 and
continuously transmitted by satellite, thus offering even more
responsiveness and capacity savings. The mapping globally broadcast
to all terminals will be stored by each terminal that will use it
if necessary upon each new transmission. Therefore, while the
system is operational, the configuration may be dynamically
optimized in the following manner: [0129] 1. the position of all
terminals is collected and stored (by being based on the
localization information sent during the last transmission); [0130]
2. the number of terminals present in each area as well as their
behavior model (probability that they will transmit a message in
the following period) will be calculated; [0131] 3. by using the
known characteristics of the satellite, and by using a statistical
model for the terminal behavior, the signal level potentially
received by the terminals in the served areas, as well as the level
of interference potentially received by the terminals in the
unserved areas are calculated for each spot beam; [0132] 4. The
size of the areas that cause the most interference (or that contain
the highest number of terminals) is reduced and, consequently, the
size of the areas that cause the least interference (or that
contain the lowest number of terminals) is enlarged.
[0133] Of course, it is entirely possible to use other algorithms
for optimization means 108. These algorithms may, for example,
utilize an exhaustive search of all possible configurations, a
limited search by branch and bound techniques or searches based on
the simplex algorithm.
[0134] It is important to note that, in the case of the W2A
satellite, a communication network operating with several million
ground terminals per cell and messages of 100 bytes each per
frequency channel is planned. Because of this, such an operation
will lead to the issuance of more than one billion messages per day
in the European coverage area. Therefore, the network according to
the invention allows such a quantity of messages to be absorbed by
combining the transmission of transmission parameter mapping
(dynamically updated) to terminals with a location at the level of
each of the terminals.
[0135] Of course, the invention is not limited to the embodiment
that has just been described.
[0136] Therefore, the invention was more particularly described in
the case of the S band but it may also be applied to other types of
frequency bands, for example, the Ka band.
[0137] In addition, even if the invention was more specifically
described for a network utilizing a GPS positioning system, the
invention is also applicable to other positioning means such as
positioning means utilizing WIFI access points or based on a GSM
type base station.
[0138] In addition, we described the invention in the case of a
global trans-mission of a single mapping to all ground terminals
("broadcast" type transmission). It is also possible to apply the
invention to a "multicast" type transmission: In this case, a first
mapping is sent globally to a first group of ground terminals (for
example, general public ground terminals) and a second mapping
different from the first is sent to a second group of ground
terminals (for example, professional ground terminals).
[0139] Even in the case of "broadcast" type transmission, data sent
with the mapping may limit the utilization of this mapping to
certain groups of terminals, or to certain services. Typically,
certain transmission parameters may be reserved for the
transmission of urgent messages, while other transmission
parameters are utilized for transmitting non-urgent parameters.
* * * * *